Processes for the production of rigid polyurethane foams are known. See, for example, U.S. Pat. Nos. 3,085,085; 3,153,002; 3,222,357; and 4,430,490.
One of the key components used to produce any foam is the blowing agent. While a number of blowing agents are known, the blowing agent most commonly used by U.S. appliance manufacturers to produce rigid foams for insulation applications today is 1,1,1,3,3-pentafluoropropane (commonly referred to as HFC 245fa). While HFC 245fa does make it possible to produce rigid polyurethane foams with advantageous physical properties, further property improvements, especially improvements in the k-factor or insulating ability, in view of increasing energy costs and the possibility of further tightening of Government energy efficiency requirements, are still being sought.
It would therefore be advantageous to develop a process for producing rigid polyurethane foams with lower thermal conductivities than the currently available HFC 245fa blown foam using no additional blowing agent(s) and commercially available materials without the need for additional equipment or process controls.
One approach to developing such a process which has not, to date, been explored to any great extent is the use of higher density foams blown with a hydrofluorocarbon blowing agent. This may be attributed to the fact that lighter weight insulating foams have been considered highly desirable for applications such as refrigerator insulation.
U.S. Pat. No. 5,461,084 discloses polyurethane foams with core densities between 2.10 and 2.36 pounds per cubic foot (pcf). The foams produced in this patent with an HFC blowing agent and no added water, however, were made with relatively large amounts of the HFC blowing agent.